1. Field of the Invention
The present invention relates to real-time recording of the translational and angular acceleration of a head and, in particular a human head and, in a most preferred implementation, the head of a living human subject in normal activity.
More particularly, it relates to a helmet-based system which is typically worn while playing a sport such as boxing or football, and to the method of recording and storing data relating to translational and angular accelerations of the person's head due to impact forces acting thereon.
2. Background of Related Art
Translational movement relates to the motion of a rigid body in such a way that any line which is imagined rigidly attached to the body remains parallel to its original position. Translational acceleration is the time rate of change of the velocity of the translational movement. Angular acceleration (also called rotational acceleration) is shown in FIG. 3. As point p moves on a circular path with radius r through angular displacement .THETA., angular velocity is the rate of change of .THETA. with respect to time. Angular acceleration .alpha..sub.2 is the rate of change of angular velocity. The tangential component of translational motion T shown in FIG. 3 is actually measured. Normal acceleration (which is a form of translational acceleration) relates to the acceleration toward the center of the circular motion.
Little is known about how a living human head accelerates in translational and angular directions in response to forces, and even less about the correspondence between specific forces and injury, particularly with respect to injuries caused by repeated exposure to impact forces of a lower level. Almost all of what is known is derived from animal studies, studies of cadavers under specific directional and predictable forces (i.e. a head-on collision test), and from crash a dummies or other simplistic mechanical models. The conventional simplistic application of known forces and/or measurement of forces applied to animals, cadavers, and crash dummies limit our knowledge of a relationship between forces applied to a living human head and resultant injury thereto.
Some conventional devices have employed modeled testing approaches which do not relate to devices which can be worn by living human beings.
When studying impact with dummies, they are typically secured to sleds with a known acceleration and impact velocity. The dummy head then impacts with a target, and the peak accelerations experienced by the head are recorded. Impact studies using cadavers are performed for determining the impact forces and pressures which cause skull fractures.
For instance, U.S. Pat. No. 4,873,867 to McPherson et al. and U.S. Pat. No. 4,691,556 to Mellander et al. disclose the use of accelerometers mounted within cavities formed in the head of a crash dummy. Viano et al. "Measurement of Head Dynamics and Facial Contact Forces in the Hybrid III Dummy" and Shea et al. "Computing Body Segment Trajectories in the Hybrid III Dummy Using Linear Accelerometer Data" disclose the placement of between seven and nine accelerometers inside a cavity formed in the head of a dummy. Pintar et al. "Experimental Production of Head-Neck Injuries Under Dynamic Forces" discloses removal of the top of a cadavers head and placement of accelerometers therein. Got et al. "Results of Experimental Head Impacts On Cadavers: The Various Data Obtained and Their Relations to Some Measured Physical Parameters" disclose the use of high speed photography and three accelerometers screwed into different positions in a cadavers skull, depending on the impact test to be performed. Nahum et al. "Impact Tolerance of the Skull and Face" disclose testing of a human skull using a single uniaxial accelerometer placed opposite a predetermined point of impact.
Other conventional devices have measured the acceleration of a living human head, but these devices have measured a specific, usually single axis of acceleration which was known beforehand with a single accelerometer placed accordingly, and/or relate to devices which are not worn in everyday practice of sports. Moreover, because these devices measure the limits of living human response to predetermined forces and the results thereof, they require many factors of safety.
For instance, Schmid et al. "From the Practice, Experience With Headgear in Boxing" discloses the use of a transistor apparatus with crystal gauges and a loop-oscillograph to measure skull accelerations. Two crystal gauges were fastened to the head by bandages, one on the occipital bone and the other on the temporal bone.
The device measured a predetermined force from a predetermined direction. Johnson et al. "Peak Accelerations of the Head Experienced in Boxing" discloses the use of one piezoelectric accelerometer held on by a scuba diving helmet. Muzzy III, et al. "Comparison of Kinematic Parameters Between Hybrid II Head and Neck System with Human Volunteers for -G.sub.x Acceleration Profiles" discloses the use of six accelerometers held within a subject's mouth. Similarly, U.S. Pat. No. 4,461,553 to Doerr et al. discloses the use of accelerometers in a mouthpiece. Ewing et al. "Dynamic Response of the Head and Neck of the Living Human to -G.sub.x Impact Acceleration" discloses a cumbersome, view-blocking device wherein a biaxial accelerometer is held in the mouth, and another is strapped over the bregma, and these are measured together with a photo-technique to determine accelerations. This device measured forces from a predetermined single direction of force. The use of a rate gyroscope held in the mouth of the subject is disclosed by Ewing et al. "Living Human Dynamic Response to -G.sub.x Impact Acceleration II--Accelerations Measured on the Head and Neck", and Ewing et al. "Torque versus Angular Displacement Response of Human Head to -G.sub.x Impact Acceleration".
Some conventional devices have required cumbersome and complex circuitry which is hardwired between the sensors and the computing device. These devices are impractical for use in actual sporting events.
For instance, Ordway et al. "The Effect of Head Position on the Analysis of Cervical Motion" discloses electromagnetic sensors attached to the top of the head with a velcro strap. In this device, a fixing vest was worn by the subject to exclude flexion and extension of the thoracic spine from the measurements, and the digitizing system was hardwired to a personal computer for data collection. U.S. Pat. No. 3,788,647 to Evans discloses the temporary use of a swing measurement system for analyzing test swings of an athlete's arm, bat or club for fitting of orthopedic devices.
Models are less desirable than measurement of a living human head during performance of the actual sport because of the uniqueness of the human anatomy and thus the limited extent to which the living human head can be modeled adequately with mechanical models or even cadavers. Moreover, modeling alone does not provide data as to the cause of an injury experienced by a specific individual. Non-living heads (i.e. cadavers) do not account for the application of muscle tension in the neck nor for muscular or pain reactions of the head. For instance, modeling the forces impacting on a persons head does not provide specific data as to an injury suffered by a particular individual, i.e., data derived from models and cadavers does not provide the means to correspond actual human injuries to the specific accelerations which may have caused the injury.
Helmets are conventional devices. It has been known to conduct drop tests of helmets using an accelerometer placed opposite the predetermined site of impact. For instance, see the drop tests performed on football helmets disclosed by U.S. Pat. No. 4,326,303 to Rappleyea, and U.S. Pat. No. 3,994,020 to Villari. However, these tests are most often destructive tests and do not provide data for a specific person while wearing the helmet for its intended use, e.g., during a football game. Moreover, these tests specifically tested helmets themselves (not the resultant force to the head), and measured thresholds for which the helmets would crack or break, not the head.
There are other devices that have been developed to measure head motions for a variety of other applications. These include: (1) In military applications, systems have been developed to monitor the orientation of a pilot's head to assist in targeting. (2) In virtual reality systems, the motion of the head and other extremities is continuously monitored to provide feedback to the computer enabling updating of images, etc. But these applications are for helmets which are extensively instrumented, must remain hardwired to the support infrastructure, typically use only one or two position detectors, and do not measure and record forceful blows to the head.
For instance, U.S. Pat. No. 4,743,200 to Welch et al. discloses a fiber optic helmet used for control of a display system. However, this system not only requires complex circuitry and a permanent fiber optic connection to large pieces of equipment, it is not used during performance of a sport, and the accelerometer is used to determine only the position of the head, not to determine translational and angular acceleration due to undetermined external forces.
U.S. Pat. No. 4,769,629 to Tigwell discloses the use of a two-position mercury switch in a motorcycle helmet to light a stop light when decelerating in the forward direction only.
Placement of a motion sensor on the head has been known.
For instance, U.S. Pat. No. 4,440,160 to Fischell et al. discloses the use of a single accelerometer in a headband for detecting whether or not the head is accelerating beyond a threshold amount. U.S. Pat. No. 4,869,509 to Lee, U.S. Pat. No. 4,502,035 to Obenauf et al., and U.S. Pat. No. 4,560,166 to Emerson all disclose a motion sensor mounted on a golfer's cap to sense improper head movement during a golf swing. However, long term exposure to continual forces can be as injurious to a head as can be a single hard blow. Conventional devices do not measure and record translational and angular forces to a living human head over a period of time of exposure, particularly where the exposure is of a low level below that which would normally cause concern for injury. For instance, continual blows to a head during a boxing match or football game may not cause injury individually but in combination may prove lethal. Head injury in these sports can have significant short and long term consequences which can be made more severe if blows to the head continue (e.g., from continued play in the same game or in a subsequent game). Thus, conventional devices which measure acceleration in a single direction, or from a single event, or only above a predetermined threshold, or in a way which does not permit use during performance of the actual sport do not provide the dynamics necessary to correlate exposure to forces to the injury caused by that exposure over a period of time.
Injuries are not the only area of study which are deficient. In sports such as boxing where the bout is scored with the number of punches of a certain force connecting to the head, scoring is made difficult by conventional observational techniques of scoring.